An example of a hydraulically actuated electronically controlled unit injector fuel system is shown in U.S. Pat. No. 5,191,867 issued to Glassey on Mar. 9, 1993. The fuel system disclosed in Glassey includes pressurized hydraulic actuating fluid which is used to open the fuel injectors, thereby causing fuel to be injected into an engine cylinder. A hydraulic pressure sensor is included to sense the pressure of the hydraulic actuating fluid and allow the system to implement closed loop control of the hydraulic actuating fluid pressure.
Although the system disclosed in Glassey adequately controls the hydraulic fluid pressure, it does not provide a means for determining when a fuel injector has failed. It would therefore be preferable to provide a hydraulically actuated electronically controlled fuel system that is able to detect a fuel injector failure.